 The study tested the efficacy of a mobile app called Mobile Messaging for Men, M-Cubed, in increasing HIV prevention and care behaviors among diverse US gay, bisexual, and other men who have sex with men, GBMSM. The app provided prevention messages in six domains of sexual health and offered ordering of at-home HIV and sexually transmitted infection test kits, receiving pre-exposure prophylaxis, PrEP, evaluations and navigation, and service locators. The study found that allocation to the intervention arm was associated with higher odds of HIV testing and PrEP use among high-risk GBMSM in three US cities. This article was authored by Patrick Sean Sullivan, Rob Stevenson, Sabina Hershfield, and others.